Construction of turbine stator blades



May 6, 1958 H. s. RAINBOW |=:r

CONSTRUCTION OF TURBINE STATOR BLADES Fil'ed May 10, 1954 2 Sheets-Sheet 1 CONSTRUCTION OF TURBINE STATOR BLADES Filed May 10, 1954 I 2 Sheets-Sheet 2 United States Patent Ghee CONSTRUCTION OF TURBINE STATOR BLADES Horace S. Rainbow and Hans J. P. B. Kahn, Coventry,

England, assignors to Armstrong Siddeley Motors Limited, Coventry, England Application May 10, 1954, Serial No. 428,736 Claims priority, application Great Britain June 1, 1953 8 Claims. (Cl. 25339.1)

This invention relates to turbine stator blades, for a gas turbine engine, of the kind in which each blade has a bolt mounting at one end, the other end being supported from a structural member of the engine in such manner as to restrain the end of the blade against circumferential movement.

The main object of the invention is to adapt a turbine stator blade of this kind to permit internal air cooling of the blade.

According to the invention, a turbine stator blade'com prises a longitudinally-ribbed or landed core which is adapted for the bolt mounting at the one end, and is supported as aforesaid at the other end, and which supports a sheath, of appropriate aerofoil configuration, with thin platforms at its ends, the appropriate sheath platform being secured, as by welding, to a correspondingly-shaped and recessed platform on the core adjacent the bolt mounting end to provide a shallow chamber communicating with the channels between the ribs or lands and with at least one air supply passage extending through the bolt mounting end of the core clear of the bolt hole. In this way it is the core with its supported integral ends (formed, for example, by casting) which takes the bending loads imposed by the gas flow.

According to a further feature of the invention, as ap plied to the ring of inlet turbine stator blades for a gas turbine engine, the radially-outer end of each blade core has a single bolt mounting, the bolt being an axiallyextending one for passing through holes in the core end and in flanges of the stator casing.

There would normally be a variation of the outside heat transfer coefficient across the blade from the leading to the trailing edge, and, to compensate for this, the quantity of cooling air passing along the respective channels between the lands is controlled, according to a still further feature, by forming the channels to be of different cross-sectional areas at their outlet ends so as to produce predetermined different flows along the respective chan nels. This can be effected by providing upstanding ridges on the core at the outlet end between the lands, the height of such ridges being, of course, less than the height of the lands but individually determined to produce the required outlet areas.

If the cross-sectional meant the cooling channels were constant throughout the length of the blade from the inlet end to the outlet, the quantity of heat transferred would vary at different points along the length 'of the blade due to variations in gas and cooling air temperatures (e. g., due to the cooling air becoming heated), with the result that the blade may not be uniformly cooled. To avoid this, according to yet another feature, the cross-sectional area of each channel is reduced along its length from the inlet end so as appropriately to increase the velocity of the cooling air as it proceeds along the channels.

This could be achieved by an appropriate increase in the width of the lands between the inlet and outlet ends, thereby reducing the width of the cooling channel; but preferably it is achieved by appropriately decreasing the 23,833,514 Patented May 6, 1958 Figure 1 is a longitudinal section through part of a turbine stator, showing one form of blade according to the invention in'section;

Figure 2 is a developed plan view on the line 2-2 of Figure 1 and showing two adjacent blades;

Figure'3 is an enlarged planview of one of the blades shown in Figure 2;

Figure 4 is a section on the line 4-4 of Figure 3;

Figure 5 is a perspective view of a blade in exploded condition and showing the sheath partly broken away; and

Figure 6 is a sectionalview on the line 66 of Figure 5 on an enlarged scale.

Figure 1 shows a blade core 11 having, at its radiallyouter end, an extension 12 clamped by a bolt 13 between flanges 14 and 15 at the adjacent ends of two rings 16 and 17, respectively, which form the outer'annular wall of the stator gas passage. The flange 15 is shown having a dog-tooth engagement at 18 with a ring 19 which is clamped by a ring of bolts 20 (one only being shown in Figure 1) extending through flanges 21 and 22, respectively, of outer casing portions 23 and 24, the dog-teeth providing circumferential location for the rings 16 and 17.

At its radially-inner end the core has an integral pin 25 slidably engaged in a radial hole of an inner mounting ring 26 which has a toothed engagement at 27, providing circumferential location, with a structural part 28 of the engine.

The core, as can best be seen from Figure 5, has a landed portion 29 of aerofoil section surmounted by a platformfiil with a peripheral flange 31. Closely fitting on the lands 32, 32 of the portion 29 is a sheath 33 the exterior of which provides the operative surface of the blade, and it has platforms 34, 35 at its ends. The plat form 34 is sealingly secured, as by welding 36 (see Figure l), to the lip 31a of the flange 31 and defines a shallow chamber 55) into which air is delivered through a pair of ports 37, 37 which straddle a hole 38, for the bolt 13, in the extension 12 and extend through the latter to its radially-outer side. From there it receives air from a passage 39 which is between the ring 16 and outer casing portion 23, the air coming from the engine air compressor (not shown). This air then traverses the channels 32a defined between the lands 32, 32 and the inner wall of the sheath 33, and is exhausted from the radiallyinner end of the balde to pass freely in the downstream direction as indicated by the arrow 40 in Figure 1.

The platforms 34 and 35 forms shrouds between adjacent blades for constraining the working fluid to take the desired path between them and the downstream ends, of the rings 16 and 26 are shown provided with respective fairings 41 and 42. At the downstream side of the fairing 42 the radially-inner end of the blade is spaced from the adjacent surface of the ring 26 so as to provide a chamber 43 with an open downstream side through which the cooling air delivered to the said chamber can be conducted away in the downstream direction as indicated by the arrow 40. g I

Figure 4 shows an arrangement in which, adjacent its radially-inner end, the core 29 is provided, between.ad-.

jacent lands, with tapering enlargements 44' whereby to reduce the cross-section of the outlet ends of the channels between the lands and the sheath. By forming these enlargements of selected heights it can be ensured that the velocity of the air along the several channels shall be such as to obtain the desired heat transfer coefficient across the blade from the leading to the trailing edge.

Obviously the air becomes heated during its passage r a.) through. the channels, and if the latter were of uniform cross-section the quantity of heat transferred would vary along the length of the blade. To avoid such variation of heat transfer the channels between the lands can, as also shownby Figure 4, be of progressively decreasing depths from the inlet to the outlet end. In this way, as the air becomesheated on its way from the inlet end it becomes accelerated towards the outlet end to assert a cooling action which compensates for its increased temperature.

As the blade sheath is attached only at the air inlet end to the core mounting, either can expand or contract radially with respect to the other--i. e., in an axial direction ofthe blade.

The lands on the core adequately support the sheath in ternally along its whole length, and bending loads applied to the sheath are therefore transferred to'the core' which is made-adequately resistant to such loads.

What we claim as our invention and desire to secure by Letters Patent of the United States is:

1. A'turbine stator blade, which is adapted to be supported at its ends from inner and outer walls of the gas thereon supporting it at each end from said walls, spaced apartlongitudinal lands on said core intermediate its ends, said lands substantially co-extensive in length with said sheath and said lands throughout their lengths supportingl y engaging the inner surface of said sheath, said core outwardly of said lands at one end formed with a laterallyextending platform provided with a peripheral flange, said platform and flange defining a recess presented towards the other end of said core, said sheath at its end adjacent said one end of said core provided with a laterally-extending platform radially spaced from the core platform and sealingly engaging the peripheral flange of the core platform so as to form a chamber, port means in said one end of said core for admitting cooling air to said chamber, and another chamber having an open downstream side and formed by a portion of said other end of said core being spaced from said inner ,wall, said sheath and lands defining channels in communication with said first chamber and for conducting cooling air therefrom to said another chamber, the cooling air then discharging from said downstream side of said another chamber.

2. A turbine stator blade as claimed in claim l'wherein said core supporting means includes one end of thecore havinga through hole for a supporting bolt, the inner of said walls having a hole therein, said core supporting means also including at the other end of the core a pin for engagement in said hole of the inner of said walls.

3. A turbine stator blade as claimed in claim 2 wherein said sheath at its end adjacent the other end of said core is provided with a second laterally-extending platform, a portion of which sealingly engages a radially extending fairing on said inner wall, said sheath platforms providing inner and outer circumferential portions ofan annular duct for directing gas from said gas passage between an annular assembly of the turbinestator blades.

4. A turbine stator blade as claimed in claim 1 wherein said channels are directed longitudinally of said blade and are separated from one another, longitudinally extending enlargements are provided on the core between the lands adjacent said another chamber, said enlargements being of different heights from the leading edge to the trailing edge of the blade to provide predetermined different flow areas along the blade for imparting different cooling characteristics from the leading edge of the blade to the trailing edge thereof.

5. A turbine stator blade as claimed in claim, 1 wherein said channels are directed longitudinally of said blades and are separated from one another, and said lands increase in width from the end adjacent said first chamber whereby to diminish the cross-section of said channels and to increase the velocity of the cooling air as it proceeds towards said another chamber for avoiding variations in heat transfer at different points along the length of the blade due to variations in temperature difference of the air and of a hot gas outside the blade in said gas passage.

6. A turbine stator blade as claimed in claim 1 wherein said channels are directed longitudinally of said blade and are separated from one another and said lands diminish in height from the end adjacent said first chamber toward said another chamber whereby to diminish the cross-section of said channels and to increase the velocity of the cooling air as it proceeds towards said another chamber for avoiding variations in heat transfer at different points along the length of the blade due to variations in temperature difference of the air and of a hot gas outside the blade in said gas passage.

7. A turbine stator blade as claimed in claim 3 wherein said channels are directed longitudinally of said blade and separated from one another, longitudinally extending enlargements are provided on the core between the lands adjacent said another chamber, said enlargements being of different heights from the leading edge to the trailing edge of the blade to produce predetermined different flow areas along the blade for imparting different cooling characteristics from the leading edge of the blade to the trailing edge thereof, said lands increasing in width from the end adjacent said first chamber toward said another chamber whereby to diminish the cross-section of said channels and to increase the velocity of the cooling air as it proceeds towards said another chamber for avoiding variations in heat transfer at different points along the length of the blade due to variations in temperature difference of the air and of a hot gas outside the blade in said gas passage.

8. A turbine stator blade as claimed in claim 3 wherein said channels are directed longitudinally of said blade and are separated from one another, longitudinally extending enlargements are provided on the core between the lands adjacent said another chamber, said enlargements being of progressively different heights from the leading edge to the trailing edge of the blade to produce predetermined different flow areas along the blade for imparting different cooling characteristics from the leading edge of the blade to the trailing edge thereof, and said lands diminishing in height from the end adjacent said first chamber toward said another chamber whereby to diminish the cross-section of said channels and to increase the velocity of the cooling air as it proceeds towards said another chamber for avoiding variations in heat transfer at different points along the length of the blade due to variation in temperature difference of the air and of a hot gas outside the blade in said gas passage.

References Cited in the file of this patent FOREIGN PATENTS 467,345 Italy Dec. 3, 1951 491,904 Canada Apr. 7, 1953 491,905 Canada Apr. 7, 1953 602,530 Great Britain May 28, 1948 619,107 Great Britain Mar. 3, 1949 1,021,265 France Nov. 26, 1952 

